This invention relates to removing cylindrical bodies from a mandrel, and in particular stripping plastic pipe from a mandrel.
Plastic pipe, and particularly fiber reinforced plastic pipe, is typically formed about a rotating mandrel as described in U.S. Pat. Nos. 3,519,520 and 3,616,063. Release agents are commonly coated onto the surface of the mandrel to assist removal of formed pipe from the mandrel. However, even with release agents, a common problem is how to strip the pipe from the mandrel without damaging either the pipe or the mandrel.
The method described in U.S. Pat. No. 3,519,520 includes grabbing an outer end of the pipe with grabber jaws which clamp onto the pipe. These jaws are mounted on a chain driven carriage which is pulled axially, thereby pulling the pipe off a free end of the mandrel.
Although this method is useful for removing pipe from a mandrel, it is not without disadvantages. In particular, the grabber jaws exert a radial force against the pipe and the mandrel. Due to this radial force, the pipe is pressed against the mandrel, thereby making it more difficult to slide the pipe longitudinally over the mandrel. In addition, plastic pipe has lower axial tensile strength than axial compressive strength. Therefore, the force which can be applied to the pipe when pulling pipe from a mandrel is less than the force which can be applied to the pipe when pushing the pipe from a mandrel.
Another method of removing pipe from a mandrel comprises applying high pressure water to one end of the mandrel to force it from the pipe. This method requires bolted construction at one end of the mandrel and time-consuming disassembly at the bolted end each time a pipe is removed. Overall, this method is slow, messy, and the constant exposure to water tends to corrode the mandrel.
Therefore, there is a need for a quick and clean method and apparatus for removing plastic pipe from a mandrel which damages neither the pipe nor the mandrel.